The present invention relates to a heatable sealing roll.
Heatable sealing rolls are used, for example, for the continuous sealing of blister packs for small pharmaceutical products. To protect the sensitive pharmaceutical products, the blister packs must be tightly sealed, for which reason very high requirements are imposed on the sealing process. It is standard practice to use heat and pressure to seal an aluminum lidding sheet coated with a heat-seal lacquer tightly to a PVC bottom sheet, the blister pockets of which hold the pharmaceutical products. There are many different ways in which the heatable sealing roll can be designed.
A typical design uses tubular heating cartridges introduced into the sealing roll. The disadvantages of this type of design, in which the measurement signals and feed voltage for the heating cartridges are transmitted via slip rings, are to be found first of all in the corrosion of the slip rings by PVC gases and in the wear to which they are subject, which can lead to uncontrolled interruptions in the measurement signals and thus in the heating of the sealing roll. In addition, the use of resistance heaters requires a large thermal mass to achieve a uniform temperature distribution. The automatic temperature control therefore operates slowly. Finally, heating cartridges are wear parts, which must be replaced after a certain number of operating hours. Because gap corrosion occurs as a result of the continuous heating and cooling, it is often not possible to replace the cartridges easily without destroying them in the process.